sounds like a corrupt os, a clean install would most likely be best. its very possible that norton product caused the problems, it did for me back in os 9.2.2, exact same thing, had to do a clean install. to boot from the cd, not recommended, insert it, shut down your mac, boot up holding down the C on the keyboard until it boots up from the disc.
have you recently , or since the problem started, installed any new software that may be causing an extension conflict?